This invention relates to improvements in cutter dies for the cross rolling machine.
The cross rolling machine for rolling and shaping a graduated shaft is conventionally constructed as illustrated in FIGS. 1 and 2. As seen in the figures, W denotes a shaped bar material; 01, 01' a pair of rolls mounted in parallel on two shafts and rotatable from a preferred drive source in the same direction and at same speed; 01a, 01'a rolling dies of a wedge shape provided on the outer peripheral surfaces of the rolls 01, 01'; and 01b 01c, 01'c 01'b cutter dies fixed on the outer peripheral surfaces of the rolls 01, 01' on both sides of each of the wedge-shape rolling dies 01, 01'. A given heated bar material W may be inserted between the rolls 01, 01' which may be rotated at the same speed in the direction of the arrows in the figure. The material W is compressed and rolled between the rolling dies 01a, 01'a and formed into a desired shape, and then cut off by the cutter dies 01b, 01'b 01c, 01'c finally taken out as a finished product. The remaining bar material may be inserted between the rolls 01, 01' through mechanical elements not shown and subjected to a subsequent rolling and shaping operation. In the same manner as described above, a bar material experiencing compression and rolling between the rolling dies 01a, 01'a and further cut off by the cutter dies 01b, 01'b 01c, 01'c, which is likewise formed into a product. These operations can be repeated continuously for rolling and shaping. The above described cutter dies 01b, 01c and 01'b, 01'c (cutter 01'c is not shown) are formed as shown in a developed view of FIG. 3 and a transverse view of its end portion as shown in FIG. 4, respectively (Cutter dies 01'b, 01'c are substantially identical as 01b, 01c and therefore not shown). Thus, it is provided that a product 02 and a long bar material 04 are cut off by the cutter dies 01b, 01'b and the product 02 and the remaining portion 03 in the forward end of the material are cut off by the cutter dies 01c, 01'c (Refer to FIG. 5). In this instance, formation of a service hole in the forward end 05 can be avoided by preforming an end 05 of a long bar material 04 into a conical shape as shown in FIG. 5, which end portion is provided with an excess portion. For this purpose, the end portions of the cutter dies 01b, 01'b have in their transverse sectional surfaces angles .beta. as shown in FIG. 4. Preferably the angle .beta. may be 15.degree.-70.degree. and particularly 45.degree. as heretofore considered appropriate.
However, in the above prior art cutter dies, the cutter dies are provided to cut into a bar material so that, when the material is cut off slowly, the oblique shaping surfaces of the cutter dies tend to extend gradually so deep as to reach the central part of the material to cause the shaping force F to act ever increasingly on the bar material. This resulted in that, as shown in FIG. 6, the product had a deficiency 07 in the shaft portion of the product 02 or a deficiency 08 inside the stepped section of the product. Hitherto, this drawback was compensated by forming the product slightly larger in diametrical dimensions than desired, such compensation partly bringing bad yield in the product. The same also applied to the case of the cutter dies 01c, 01'c.
To overcome the drawback in the conventional cutter dies, the inventors have proposed novel cutter dies for the cross rolling machine, which construction is characterized in that a cutter die consists of a shaping surface and a finishing surface and the shaping surface may have its width increasingly smaller and the height larger closer toward the end portion of the shaping surface.
Formation of the described shaping surface may be illustrated with reference to the accompanying drawings, particularly to FIGS. 7-12.
In FIG. 7, numeral 1 denotes rolls, 2 end portions of wedge-shaped rolling dies attached to the outer peripheral surfaces of the rolls, 3 cutter dies on the outer peripheral surfaces of the rolls 1 on the outside of one of the rolling die end portions 2, and 3' cutter dies on the outer peripheral surfaces of the rolls 1 on the outside of the other of the rolling die end portions. The cutter dies 3 serve to cut off the product 02 from the bar material 04 and the cutter dies 3' cut off the product 02 from the remaining portion 03 in the forward end of the bar material respectively. Each of the cutter dies 3 are constituted by a shaping surface 3a and a finishing surface 3b, which are connected by a zenith line 7, and each of cutter dies 3' are constituted by shaping surface 3'a and finishing surface 3'b connected by a zenith line 8, respectively. The above-mentioned zenith lines 7, 8 are moderately sloping curves more inclined closer to the wedge-shape dies 2, nearer the end portions of the cutter dies 3, 3'. That is, the width of shaping surfaces 3a, 3'a become increasingly smaller toward the end portions of the cutter dies 3, 3' and the finishing surfaces 3b, 3'b are formed to have their width increasingly larger. The shaping surfaces 3a, 3'a also may have their height increasingly larger in the end portions of the cutter dies 3. As shown in the enlarged views of FIG. 11, (I), (II), and (III), the shaping surface 3a may have the width increasingly smaller as shown respectively by a.sub.0 -b.sub.0, a.sub.1 -b.sub.1, and a.sub.2 -b .sub.2 closer to the end portion of the cutter dies. The height of the cutter dies is formed increasingly greater as shown respectively by h.sub.0, h.sub.1, and h.sub.2 also closer to the end portions of the cutter dies. The above described shaping surface 3a is deeply cut into the central part of the material while shaping the bar material during rolling and shaping operation to accomplish the cutting and separation of the material 04 and the product 02. The shaping is thus achieved by the shaping cutter substantially in contact with the material and taking a part of the material to be transferred.
The finishing surface 3b, on the other hand, as shown in FIG. 11, (I), (II), and (III), may have increasingly larger widths closer to the end portions of the cutter dies 3 as shown by b.sub.o, b.sub.1 -c.sub.0, and b.sub.2 -c .sub.1 respectively at points on the material. This finishing surface 3b can not serve to transfer volume of the material during rolling and shaping of the material. The shaping surface 3a is finished up in the way slightly contacting the surface shaped by the described shaping surface 3a. The angles .beta..sub.1, .beta..sub.2 made respectively on the inclined surfaces of the shaping surface 3a and the finishing surfaces 3b may normally be 15.degree. to 70.degree.. Experiment provided 25.degree. for .beta..sub.1 and 45.degree. for .beta..sub.2 respectively which were taken most appropriate for the angles. In the similar way, the angle of inclination in the shaping surface 3'a and the finishing surface 3'b may be adequately selected. Although omitted from the drawings, the cutter dies of the same construction as above described may be likewise provided in the other rolls of the cross rolling machine.
The cutter dies as conventionally proposed and having the construction as above described are arranged such that the product 02 and the bar material 04 can be rolled and shaped with a pair of rolls into a stepped shaft with flanged parts and they are cut off separately. The shaping surfaces 3a of the cutter dies 3 are slowly cut into the material. The product 02 and the bar material 04 are cut off separately on the shaping surface 3a. In this instance, the material is extended outwardly to balance with the shaping force F.sub.0 (FIG. 9) of the shaping surfaces 3a in an amount corresponding to the volume of cutting of the shaping surface 3a deep into the material. On the other hand, the finishing surface 3b provides finishing only in the shaping surface 3a without transferring the volume of the material while the shaping force produced from the finishing surface 3b is acting upon the bar material. Accordingly, the shaping force F.sub.0 is so greatly reduced as compared with the conventional cutter dies so that the product may not have a deficiency in the surface as heretofore encountered.
The above description also applies to the shaping surface 3'a and the finishing surface 3'b as well.
The inventors have thus manufactured a number of stepped shaft products by use of the described cutter dies for the cross rolling machine. After continued manufacture of products, a disadvantage was found in the cutter dies in that the spring shaping surface of the cutter dies (a.sub.2 -b.sub.2, particularly a.sub.2 in FIG. 11 (III) ) would wear out gradually and the separation of the product from the material was not achieved effectively.
This disadvantage can be removed by the inventors in an attempt to surely separate the product from the material even when any wear would remain in the cutter dies.